dbx 14/10 graphic equalizer

Although most audio perfectionists look down with scorn on equalizers, there are times when the benefits of such devices can outweigh their disadvantages. I discussed the pros and cons in my review of the Accuphase G-18 in Vol.11 No.4, but a brief recap here won't be amiss.

Properly used, a suitable equalizer can often improve the listenability of mediocre recordings (footnote 1), and can offset some of the deficiencies of many loudspeakers. Improperly used, an equalizer can undo all of the potential for fidelity that your system has to offer, and even when not used at allwith all its controls set for Flatall of them cause a certain amount of veiling and loss of depth. With a good one, though, the signal degradation is small enough to be outweighed by the benefits it can bring, andif installed in the preamp's Tape Monitor loopit can always be switched out when it isn't needed (footnote 2).

There are two basic kinds of equalizers: system equalizers and program equalizers. Because real-world loudspeakers in real-world rooms tend to generate lots of narrow frequency-response peaks and dips, the first requirement for a system equalizer is that it have high resolution. That is, it must have enough controllable bands, of sufficiently narrow width, to allow it to pull down a peak without unduly affecting the adjacent areas. The best ones (very rare) have 1/10-octave resolution, which means about 100 bands for each channel, while an excellent one will typically have 30 1/3-octave bands per channel. And this is precisely why a good system equalizer doesn't make a good program equalizer. Two hundred controls, or even 60, are just far too many to have to contend with every time you change records.

For program equalization, the resolution requirements are far less stringent. In fact, for most audiophiles (except, of course, those reading this magazine), a pair of well-designed tone controlsbass and treblewill do a more than adequate job of program correction. Most of the problems afflicting recordings are spectral aberrations, affecting a wide range of bass and/or treble frequencies, and ordinarily tone controls are best at compensating for these problems. A more critical listener, however, may observe that a recording has too much midbass and not enough deep bass, or has a mid-treble peak and a normal extreme-high-end balance. Clearly, no conventional tone controls can cope with either.

It is generally conceded that program equalization is best accomplished with a so-called octave equalizerone that offers 10 or 12 octave-wide controllable bands. On a unit having separate controls for each channel, that's still 20 to 24 knobs to operate when you change records, but when you consider that only six or eight of those per channel may have to be changed from one record to the next, it becomes reasonably manageable. The ideal, of course, would be to use ganged controls, where one knob affects both channels simultaneously, but that sacrifices the ability to make different adjustments in the two channels. Or at least, it usually does. In the case of the dbx 14/10, it doesn't.

The dBX 1410
The 14/10 is one of the most sophisticated graphic equalizers on the consumer market today. It is sort of a hybrid device, combining the functions of a system equalizer and a program equalizer. It divides the lower half of the audio spectrum (where most loudspeaker/room-induced response irregularities occur) into half-octave bands and the upper half into one-octave bands, and has 14 knobs which can either control both channels at once or either channel individually. The knobs are actually small lever switches which raise or lower the gain of their controlled band electronically, depending on whether they are pushed up or down. The front-panel LED display shows (as +1dB or 1dB) where each control is set, and the rate of change in each band switches from slow to fast if you hold the knob for more than a couple of seconds. At one end of the display is a continuous signal-level monitor, and the whole LED panel can also be switched to display a 14-channel real-time analyzer (RTA) readout, with vertical bargraphs showing signal amplitude within each band. A switch allows the RTA to monitor either the line signal coming into the equalizer, or the output from its own microphone (supplied). The RTA offers two display-response speeds: slow and fast. The former makes it easier to observe response readings, the latter is for checking peak signal levels. A hold button can be used to put either display into a storage mode which "freezes" the highest-amplitude reading in each band until the button is depressed a second time to release them.

Operation
Connected to its calibrated condenser microphone, and supplying its own pink-noise signal to the system, the 14/10's RTA can be used to measure and display the audio system's frequency response in the listening room. Then if you push the appropriate buttons, the device will automatically equalize the system for the flattest possible amplitude response, and show the resulting EQ curve on the display. Because pink noise has continually varying level in each octave, each eventually averaging out to flat, it takes upward of 30 seconds for the computer to ascertain exactly what the RTA is reading and to equalize for it. The RTA auto-ranges over a fairly wide range in normal use; that is, it adjusts its sensitivity to the signal level so that the display is always more or less vertically centered. For auto EQ, though, the device requires that the pink-noise signal be above a certain threshold. There's a volume control for the pink-noise signal, and if this is not set high enough, a red light next to the Average button will flash on and off for a few seconds after you depress the button. If the level is adequate, the red light stays lit until the auto EQ is completed.

The RTA or the auto-equalization function can work on either channel or in both simultaneously, and once you have the EQ curve you want, you can assign it to any one of 10 numbered front-panel buttons for later recall. Another button restores the equalizer to flat response, but all stored curves remain in its memory, even when it is turned off or unplugged from the wall outlet. A lithium battery preserves the stored data during power-off periods, for up to a claimed seven years.

And that's not all. There's even an averaging function, which allows you to call out several stored curves, as might be made from a number of different microphone positions, and average them out into one. And if you want one or two of those curves to carry more weight in the averaging process than the others, there is even provision for doing that. Averaging can be done with the automatically derived curves, or from ones you set up manually on the basis of listening, or from a combination of both.

I tried EQing two speakers I had on hand that have sounded as if they had frequency-response-related problems. In both instances, the sound was dramatically improved. This may not be the best way of compensating for mediocre speakers, but at $1300, it may be the cheapest. But, you may ask, doesn't a system equalized to measure flat at the high end sound tipped-up? Yes, it does, but dbx has thoughtfully taken that into consideration too, by providing a High-Frequency-Rolloff (HFR) button that adds the necessary HF correction. Note also that the equalizer will always try to flatten out the low end too, as indeed it should, but that if your system has little output below 40Hz, the auto EQ will boost that bottommost octave to the 14/10's +12dB limit. If this happens, do not take its advice in this regard; 12dB of boost at 31Hz will very definitely overload and possibly damage your woofers, your amplifier, or both. Pull that control down to, say, +3dB, then, if you wish, push it up a dB or so at a time until you start to hear the woofers bottoming out (or the amplifier overloading occasionally) on deep bass; then back it down a couple dB and leave it there, putting the revised curve into storage.

There is no advantage to doing the system EQ manually. The automatic EQ gives the same results in a fraction of the time, and sets the level properly as well. (Manual EQ usually results in the equalizer sounding much softer or louder than the straight-through signal.) Also, pay attention to the fact that one mike position will not give you an accurate assessment of what's going on response-wise. You must take several EQ runs, from different mike positions near where your ears will be, then average them; the more different mike positions you use, the better the EQ will be.

What about carrying out system EQ by ear? This is not recommended, unless you're a much better judge of recorded sound than most audiophiles. And consider: You don't really know what any of those favorite recordings of yours are supposed to sound likecertainly not well enough to EQ your whole system with them. It's best to do the room EQ (if at all) using the mike and the RTA or the auto-equalizer, and then store it in Register 1. The HFR correction, by the way, can be added to your final EQ and stored along with it, so the corrected curve comes up with your No.1 button. You can then call this up as the "default" each time you fire up the system, and use it as the starting point for any program EQing you wish to do.

Of course, there's nothing that says you must use the system-EQ feature. It's just there if you need it. A better approach would be to use other means, such as loudspeaker-driver balance adjustment, to get the response as flat as possible, using the RTA as a means for monitoring your progress. In fact, this is a wise thing to do first even if you do plan to EQ the system with the 14/10. But the unit does cause some signal degradation, even though it is slight. The previous 10-band, 1-octave 10/20 version of this equalizer had a slightly murky quality to its sound; this does not. Yes, it does add a small amount of veilingprobably more than you would care to tolerate when listening to, say, a Sheffield or Wilson Audio or Reference Recordings disc, but you shouldn't need to EQ those if your system is pretty close to being flat to begin with. If it isn't, you may prefer its sound with the equalizer in, veiling or not.

For program EQ, you must rely on your ears, because music never has a flat frequency response. But you don't necessarily have to do it for every record that needs it. Apart from storing different curves for averaging, the curve-storage registers and callout buttons have another very useful function: They can eliminate, most of the time, the necessity for laboriously resetting the EQ manually for different recordings. Each time you encounter a recording that needs correction, do it by ear (starting with the system-EQ curve if you choose) and store the result in one of the vacant memories. Then, next time a bad recording comes along, you can try each stored curve before manually doing another and storing it. There are 10 memories, and 9 plus your start-up button No.1 should be enough for just about any recorded response aberration. You can even copy a curve from one memory into another, by calling it up into the equalizer from one and then storing it in the other. This way, you can "organize" your curves so that the low-numbered buttons are for, say, low-boost curves and the high-numbered buttons are for high-cut curves. This will avoid having to punch all nine before you find something approximating what you need. You can then tweak that one if necessary, but you're not obliged to store it if it's similar to another that will be used more often.

Conclusion
This well-thought-out and well-engineered product has got to be one of the most versatile and usable graphic equalizers of them all. Some others will EQ a system with more refinement, and some will do almost as well for program equalization, but I don't know of another that is this effective and this easy to use. The dbx 14/10 is highly recommended to anyone whose audio religion it doesn't offend. But do use it with discretion, or it will do more harm to your sound than good.

Footnote 1: The philistine audio purist's view is that an audiophile has no business listening to mediocre recordings. The artistic, sensitive, music-lover's view is that some recorded performances are good enough to listen to from Edison cylinders, even the monophonic ones, and that any device which can make the experience less onerous is worthwhile.J. Gordon Holt

Footnote 2: All equalizers, however, introduce time-domain distortion. Though this is conventionally held to be inaudible, I do not like the idea of using something which interferes with the purity of the signal.John Atkinson

Do you think just to add a little bit more highs tweeter extension in my Gershman Avantgarde speaker, a DBX EQ would be good without changing the holographique realism sound ? Or would it be better to change internal speaker components, or change my audioresearch LS 26 preamp for another preamp treble control ? Thank you very much for your advice Simon PS I am getting older and one of my ear is not as good as I was younger